1. Technical Field of the Invention
The present invention is directed to the field of data communication networks. More specifically, the invention provides a system and method for packet data transport in a ring network that is particularly well-suited for transporting asymmetrical data flows from a common point source coupled to the ring network, such as an Internet gateway connection, to a plurality of downstream local nodes. In such a configuration, the vast majority of data packets flow from the Internet gateway connection to the local nodes, and only a minor number of data packets flow back from the local nodes to the Internet gateway connection.
2. Description of the Related Art
Ring networks are well known in the data communication art. Typical ring systems include Fiber Distributed Digital Interface (xe2x80x9cFDDIxe2x80x9d) rings, token-ring structures, and more recently Synchronous Optical Network (xe2x80x9cSONETxe2x80x9d) rings. A ring network typically includes a plurality of network nodes coupled together by one or more data communication channels (or paths). These network nodes may, in turn, couple to local nodes or networks, or may couple to other ring structures.
In a SONET network, the network nodes can be logically connected by a plurality of virtual paths that coexist on the one or more physical network connections that couple the nodes. Each virtual path may include a plurality of virtual channels, wherein each virtual channel transports packets (or cells) that are formatted according to the SONET standard format, which is known as the Synchronous Payload Envelope (xe2x80x9cSPExe2x80x9d). A SONET system incorporating virtual paths and virtual channels between the network nodes is disclosed in commonly-assigned U.S. patent application Ser. No. (S/N) 09/324,244, the disclosure of which is hereby incorporated into this application by reference. The SPE further defines the data cells as overhead and payload sections. Overhead information is used to maintain the operation and maintenance of the network, whereas payload information represents the deliverable information of the system being transported in the particular virtual channel. The physical network connection spanning the network nodes may include one or more fiber optic connections. In some network topologies, a single fiber carries payload information in both directions around the ring, whereas in others there is one fiber for one sense of direction, and another fiber for the other sense of direction. In a SONET ring network these two senses of direction are typically referred to as the east and west directions of the ring.
One important concept in ring network design is path protection switching. Path protection switching involves sensing when a fault has occured on the ring network and routing data traffic to accomodate the faulty connection. In some ring systems, a separate path protection channel or connection is provided so that if the main data path is severed (or otherwise inoperative), the system switches traffic onto the protection channel. However, these systems require a separate physical channel between the network nodes, as well as additional hardware to support the path protection channel. Moreover, if the path protection channel (or connection) is physically routed in proximity to the main connection between the nodes (as is common), then a fault (such as a fiber cut of the main connection from a back-hoe or other heavy machinery) will likely result in the path protection channel being faulty as well. A unique xe2x80x9ctransmitter-basedxe2x80x9d path protection switching system and method are disclosed in commonly-assigned U.S. patent application Ser. No. 09/324,244, the disclosure of which has been incorporated into this application by reference.
Another important concept in ring network design has emerged recently, and relates primarily, but not exclusively, to the problem of transporting Internet-type data between a plurality of users and a common Internet gateway access node. In a SONET ring network, a plurality of point-to-point connections are typically supported between the network nodes in the ring. These dedicated, point-to-point connections typically provide a great deal of bandwidth. However, one problem with using these types of point-to-point connections for Internet data relates to the fact that with the exception of certain high-traffic periods of time, much of the bandwidth dedicated to the point-to-point connection is wasted.
Another problem with routing Internet-type data over a ring network comprising a plurality of intermediate network nodes is latency, particularly downstream latency. Downstream latency is a term that describes the amount of time it takes to communicate data packets from a common gateway connection point, such as an Internet gateway, to the local nodes (i.e., customers) that are coupled to the network nodes of the ring network. Upstream latency is a term that relates to time delay in the other direction, i.e., from the local nodes to the gateway. Downstream latency is a particularly important issue for Internet applications because of the inherent asymmetry of the data flow. Because most Internet-type applications are heavily skewed towards downloading information, as opposed to uploading, it is particularly important to minimize the downstream latency through the network nodes.
One presently known attempt at transporting data packets over a ring network is ATM (Asynchronous Transfer Mode) over SONET. In this type of implementation, however, the data packets must be fully buffered at the network nodes before the node can determine whether to drop the ATM information to a local node, or to forward this information on to another network node. This buffering stage in the forwarding mechanism of ATM over SONET is slow, and thus increases the latency through each network node of the ring. This structure is generally known as a store-and-forward approach, and is also typically employed in many types of packet router products. These router products also suffer from high-latency when used in the downstream data path of a ring network.
A system and method for transporting data packets in a ring network includes a plurality of network nodes having a protection switching agent and at least one fast downstream path circuit that provides a low-latency packet cut-through function for forwarding packets from an upstream node to a downstream node. The network nodes include three interfaces, two interfaces for coupling the network node to other network nodes in the ring network, and a third interface for coupling the network node to a local node. A plurality of virtual paths are provided between a data packet gateway, such as an Internet gateway, and the local nodes that are coupled to the network nodes of the ring network. A virtual channel identifier is embedded within data packets transported on the network so that the protection switching agent in each network node can determine whether to route received data packets to the local node, or to the low-latency cut-through downstream path circuit.
According to one aspect of the invention, a SONET ring network is provided for transporting Internet data packets between an Internet gateway and a plurality of add/drop multiplexer nodes organized in a ring topology. The ring network includes: (A) a plurality of local nodes coupled to the add/drop multiplexer nodes, wherein the ring network is provisioned such that a virtual channel is formed between each local node and the Internet gateway through the plurality of add/drop multiplexer nodes; (B) a plurality of virtual channel identifiers embedded within the Internet data packets, each virtual channel identifier being associated with a particular virtual channel formed between a local node and the Internet gateway; and (C) wherein each add/drop multiplexer node includes: (1) east and west SONET agents for transmitting and receiving SONET data signals to and from two other add/drop multiplexer nodes; (2) east and west packet-over-SONET agents for processing the Internet data packets transported within the SONET data signals; and (3) a protection switching agent including an east-to-west fast downstream circuit, a west-to-east fast downstream circuit, and a local add/drop interface circuit, the fast downstream circuits including a copy circuit and a fast cut-through packet filter, and the local add/drop interface circuit including a drop-side packet filter. In this network, the protection switching agents are configured to route received Internet data packets to either the east-to-west fast downstream circuits or the west-to-east fast downstream circuits, and the copy circuit is operative to duplicate the received Internet data packets to the fast cut-through filter and the drop-side packet filter, which filter the Internet data packets based on the embedded virtual channel identifier.
According to another aspect of the invention, a ring network is provided that includes: (i) a plurality of network nodes coupled in a ring structure, wherein one of the network nodes is coupled to a data packet gateway, and the remaining network nodes are coupled to local nodes; (ii) a plurality of virtual channels formed between each local node and the data packet gateway through the plurality of network nodes; and (iii) a plurality of packet forwarding/dropping agents operating at the network nodes. Each of the packet forwarding/dropping agents further includes: (a) at least one fast downstream path circuit for forwarding data packets from one network node to another network node in the ring network; and (b) a local add/drop interface circuit for dropping packets to the local node coupled to the network node. In this network, the packet forwarding/dropping agents route received data packets to either the fast downstream path circuit or the local add/drop interface circuit by examining a virtual channel identifier embedded within the data packets.
Still another aspect of the invention provides a SONET Add/Drop Multiplexer (ADM) having three interfaces, an east SONET interface, a west SONET interface, and a local add/drop interface. The SONET ADM of the present invention preferably includes: (A) east and west SONET agents for sending and receiving SONET data signals to and from the ADM and two other SONET ADMs coupled to the east and west SONET interfaces; (B) east and west packet-over-SONET (POS) agents coupled, respectively, to the east and west SONET agents for transporting data packets within the SONET data signals; and (C) a protection switching agent including two fast downstream data path circuits, one fast downstream data path circuit coupling the west POS agent to the east POS agent and the other fast downstream data path circuit coupling the east POS agent to the west POS agent.
In this configuration, the protection switching agent of the SONET ADM routes received data packets to either of the two fast downstream data path circuits or the local add/drop interface by examining a virtual channel identifier embedded into the data packets.
Another aspect of the invention provides a method of transporting data packets in a ring network. The method includes the following steps: (a) forming a plurality of virtual paths between a data packet gateway node and a plurality of local nodes through a plurality of network nodes that form the ring network; (b) providing a virtual channel identifier within the data packets transported to and from the gateway node and the plurality of network nodes, wherein the virtual channel identifier identifies the particular virtual path to which the data packets are associated; and (c) filtering the data packets at the network nodes by examining the virtual channel identifiers to determine whether to drop the data packets to an associated local node or to pass the packets through to another network node.
It should be noted that these are just some of the many aspects of the present invention. Other aspects not specified will become apparent upon reading the detailed description set forth below.
The present invention overcomes the disadvantages of presently known ring-based networks that transport Internet-type data, and provides many advantages, such as: (1) optimized for ring-based access systems; (2) provides a low-latency downstream cut-through mechanism; (3) easily reconfigurable in response to partial network failures; (4) optimized for asymmetrical data flows, such as Internet-type data; and (5) makes better use of system bandwidth than point-to-point connections by providing a means for sharing downstream bandwidth between a plurality of virtual channels.
These are just a few of the many advantages of the present invention, which is described in more detail below in terms of the preferred embodiments. As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments set forth below are to be regarded as illustrative in nature and not restrictive.